Three-dimensional (3D) computer graphics systems, which can render objects from a 3D world (real or imaginary) onto a two-dimensional (2D) display screen, are currently used in a wide variety of applications. For example, 3D computer graphics can be used for real-time interactive applications, such as video games, virtual reality, scientific research, etc., as well as off-line applications, such as the creation of high resolution movies, graphic art, etc. Typically, the graphics system includes a graphics processing units (GPU). A GPU may be implemented as a co-processor component to a central processing unit (CPU) of the computer, and may be provided in the form of an add-in card (e.g., video card), co-processor, or as functionality that is integrated directly into the motherboard of the computer or into other devices, such as a gaming device.
Typically, the GPU has a “graphics pipeline,” which may accept as input some representation of a 3D scene and output a 2D image for display. OpenGL® Application Programming Interface (API) and Direct3D® Application Programming Interface are two example APIs that have graphic pipeline models. The graphics pipeline typically includes a number of stages, one of which is texture mapping. Texture mapping allows detail, surface texture, or color to be added to fragments being rendered. In this process, a texture map is applied to the surface of a shape. In some systems, a texel (texture element or texture pixel) is the fundamental unit of texture space. When texturing a 3D surface, the texture mapping process maps texels to appropriate pixels in the output 2D image.
Processing the texture maps to produce the output 2D image consumes valuable GPU time. Therefore, techniques such a mipmapping have been developed. Mipmapping involves storing a texture map and several reduced level of detail (LOD) versions of the texture map. For example, maps with ¼ the detail of the original, 1/16 the detail, etc. may be stored in the texture memory. Mipmaps increase the efficiency of rendering by decreasing the workload on graphics pipeline stages. For example, if rendering the scene only requires a version of texture map that has little detail, then one of the less detailed maps can be accessed from texture memory rather than taking the time to filter a detailed version.
Typically, a limited amount of memory is used to store the texture map(s). Therefore, in some cases, the desired LOD of the texture might not be available in the texture memory. For example, the application (e.g., video game) might attempt to render with more detail than maps available in the texture memory. In this case, one option is to render the scene with less detail than desired. Alternatively, additional time might be consumed loading the desired LOD for the texture into texture memory. In some cases, there might not be any maps of the desired texture stored in texture memory. Therefore, the only practical option may be to take the time to load the texture into texture memory. Furthermore, since the size of the texture memory is limited, working with extremely large texture maps can be difficult.